Effect of inter-row sod system on the contents and availability of soil nutrients in a kiwifruit orchard

Abstract:【Objective】Soil organic matters and nutrients are fundamental for sustainable kiwifruit production. Clean tillage is the conventional soil management practice in the orchard. Long-term clean tillage in the orchard may decrease soil water retention, increase surface roughness and limit weed growth,therefore alleviating root limitation caused by competition for soil nutrients and water. Inter-row sod system is recommended as an advanced soil management practice in the orchard, which can promote soil organic carbon retention, reduce soil water evaporation, and minimize soil physical disturbance.However, little is known about whether the contents of soil organic matter and nutrients in the orchard with sod are sufficient for plant growth. Furthermore, different grass species possess different effects on soil nutrients in the orchard. Thus, it is critical to choose the right grass species to ensure the balanced supply of soil organic matters and nutrients in the orchard. In order to provide a theoretical and practical basis for improving soil fertility by grass growing techniques in the orchard, the effect of inter-row planting white clover(Trifolium repens), ryegrass(Lolium perenne) and the natural weed in the kiwifruit orchard were studied on the contents and availability of soil organic matters, as well as macro-and micro-elements.【Methods】Soil samples at depths of 0-20 cm and 20-40 cm were collected from the kiwifruit orchard with white clover, ryegrass, the natural weed as well as the clean tillage(control) at Jinshan District, Shanghai. Total soil organic matter, available macronutrients(alkaline hydrolytic nitrogen, available phosphorus and available potassium), available micronutrients(iron, manganese, copper and zinc) were determined. The effective index(Ei) of every nutrient element in the soil was calculated to evaluate soil nutrient availability in the kiwifruit orchard with grass. The soil fertility per unit were evaluated according to the classification criterion for soil nutrient.【Results】In the kiwifruit orchard, inter-row sod with ryegrass could significantly increase the soil organic matter content at 0-40 cm soil layer, corresponding to 11.73% at 0-20 cm soil layer and 34.86% at 20-40 cm soil layer, respectively, in comparison with the control. Inter-row sod with white clover could also enhance the soil organic matter content at 0-40 cm soil layer, but the difference was not significant in comparison with the control. The alkaline hydrolytic N content at 0-20 cm soil layer was significantly enhanced by inter-row sod with white clover(68.03%), ryegrass(54.70%) and the natural weed(65.37%) compared to the control,whereas the alkaline hydrolytic N contents at deeper soil layers were not significantly enhanced by interrow planting grass in the kiwifruit orchard. Inter-row sod system significantly reduced the available P content at 0-20 cm soil layer, with declining percentages being up to 53.07%, 18.07%, and 7.23% for growing white clover, ryegrass and natural weed in comparison with the control. However, the available P content at 20-40 cm soil layer was not significantly affected by inter-row sod. Inter-row sod could significantly enhance the available K content(by 22%) at 0-20 cm soil layer compared to the control,whereas the available K content at 20-40 cm soil layer decreased by 26.92% with ryegrass. The available K content at 0-40 cm soil layer decreased significantly by inter-row sod with white clover and natural weed. For micronutrient elements, inter-row sod with white clover could enhance available contents of Fe, Cu and Zn, whereas only the available Zn content(31.61% and 22.92%, respectively) at 0-40 cm soil layer increased significantly by inter-row sod with white clover compared to the control. The available Fe content at 0-20 cm soil layer with ryegrass was significantly enhanced(by 35.52%) in comparison with the control, whereas natural weed had no significant effect on available contents of soil micronutrient elements. According to the criterion for soil nutrients classification, contents of soil organic matter, alkaline hydrolytic N, available P, Fe, Cu and Zn contents were higher than the critical value(Ei>1) at 0-40 cm soil layer of the kiwifruit orchard with grass, whereas the available Mn content was lower than the critical value(Ei<1). The results suggested that soil organic matter, macronutrients and micronutrients(except Mn) were sufficient, but Mn was generally deficient at 0-40 cm soil layer of the kiwifruit orchard with grass.【Conclusion】Inter-row sod with ryegrass in the kiwifruit orchard had a best effect on the improvement of soil organic matter and macronutrients at 0-20 cm soil layer, whereas interrow sod with white clover had a best effect on the improvement of micronutrients at 0-20 cm soil layer.Inter-row sod system could not enhance the available Mn contents in the kiwifruit orchard. In order to enhance the kiwifruit production, the Mn fertilizer should be properly applied in the soil of the kiwifruit orchard interplanted with grass.